D.H.
My 4th child walked at 12 months, but her brothers walked much earlier. I thought I'd tell you about my sister's kids. Her oldest didn't walk until he was around 17-18 months old. I remember, he would ROLL all over the floor to get where he was going. There were no problems, he just wasn't ready.
Her second child was a bit different. She had problems with her legs or feet, or something...can't remember...anyway, once they took her to the chiropractor, she began crawling, walking right after that. I guess she was out of sorts with her body and the Chiropractor fixed it and helped her on her way. She was in pain before and couldn't do what she wanted to do.
Is your screaming because she doesn't want to or is there an actual problem? Just a thought.